Composited multiplex transmission system



, L. ESPENSCHIED COMPOSITED MULTIPIQEX TRANSMISSION SYSTEM Filed July 29 1919 2 Sheets-Sheet 1 ZbMu/lzkale fl a w INVENTOR.

M f ATTORNEY 3m 13, mzs. 11522 586 L. ESPENSCHIED COMPOSITED MULTIPLEX TRANSMISSION SYSTEM Filed July 29, 1919 I 2 Sheets-Sheet 2 zbMlzzzvle fiyawy Source IN VEN TOR. 7

jZZwmsa/z ATTORNEYS.

Patented Jan. 13, 1925 UNITED STATES PATENT OFFICE."

LLOYD ESPENSCHIED, 01E HOLLIS, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

COMPOSITED MULTIPLEX TRANSMISSION SYSTEM.

Application filed July 29' To all whom it may concern:

Be it known that I, LLOYD ldsrnxsorrnsu, residing "at Hollis, in the county of Queens and State of New York, have invented cer- 5 tain Improvements in Composited Multiplex Transmission Systems, of which the following is a specification.

This invention relates to transmission systems and more particularly to multiplex transmission systems employing carrier currents.

Where multiplex transmission is secured by the use of carrier currents a plurality of carrier frequencies are transmitted over a common transmission line, the carrier frequencies being separated sufiiciently to prevent interference and each frequency being assigned for use as a separate channel of con'nnunication so that signals, such, for instance, as telephonic variations may be transmitted by impressing them upon the carrier frequencies. vSeveral channels may thus be superposed upon a common transmission line and each channel performs the functions of an ordinary telephone transmission line.

In ordinary telephone transmission it is usual practice to transmit over the line, in addition to the usual telephone currents, signaling currents, such as, for instance, D. C. Morse currents. This is accomplished by the use of the so-called composite sets for separating the telephone currents from signaling currents of other characters. In order to obtain the maxin'uim service from each carrier communication channel, it is desirable that the channel be utilized for the transmission of Morse or other signaling currents in addition to the telephone currents. therefore one of the objects of this invention to superimpose upon each channel of a multiplex carrier current system, both telephonic signals and signals of a different character, such as Morse signals. Another object of the invention is to provide means, whereby the transmission currents of carrier frequency may be simultaneously modulated in accordance with a plurality of signaling currents. the invention is to provide means, whereby a plurality of signals, which have been simultaneously impressed upon the same carrier current, may be separated after transmis- It is' Still another object of 1919. Serial No. 314,073.

sion to a distant point. It is also an object of the invention to provide an arrangement whereby direct current impulses of opposite polarity may be translated into carrier frequency currents having the same amplitude and frequency for waves of opposite polarity, but the carrier currents corresponding to a direct current of one polarity being opposite in phase to. those corresponding to direct current of the other polarity. The invention also contemplates translating a carrier current having the characteristics just described into direct current impulses of opposite signs. Other and further objects of the invention will be apparent as-the description of the invention proceeds.

The frequencies transmitted over the channels of a carrier telephone system are those of the individual carrier frequencies, modified in frequency by the voice frequencies. Where, for instance, four channels having frequencies of 10,000, 15,000, 20,000

and 25,000 cycles, respectively, are employed,

the 20,000 cycle channel is modified by the voice frequency so that it varies from instant to "instant; in accordance with the voice frenquencies from 20,000 cycles minus 2,000 cycles to 20,000 cycles plus 2,000 cycles (2,000 cycles being taken as the extreme of the telephone frequencies employed). \Vhere a system is employed in which the carrier frequency and one side frequency is suppressed, only the frequencies above or below 20,000 cycles would be transmitted. If or instance, if the frequencies from 20,000 cycles up are suppressed by means of a band filter, only frequencies ranging between 18,000 and 20',- 000 cycles would be transmitted.

The operation of translating an ordinary telephone circuit into a carrier channel may be regarded as being that of merely elevating the frequency band occupied by the telephone circuit to a higher position inthe broad frequency scale where it occupies a band of frequencies of the same Width as it did at the-ordinary telephone frequencies; that is, the several telephone circuits fitting into a carrier system may be regarded as being merely shifted in frequency from their absolute values, the different circuits being displaced by different'a'mounts in frequency so that they do not overlap in the carrier frequency, scale. From this conception it by the usual methods employed in compositmay be readily appreciated that the low frequency band of each telephone circuit which is so shifted may extend down to zero frequency and include such channels as are ordinarily superimposed upon a telephone circuit between zero frequency'and the lower edge of the ordinary telephone band, say 300-cycles. The principal among such channels is, of course, the D. C. channel which requires a frequency band for ordinary manual Morse operation from zero fre quency to 50 or 100 cycles. Other low frequency signaling channels, such, for instance, as a channel for the transmission of ringing current ma Y be included between the Morse channel an the lower edge of the tele hone band.

I we imagine the entire range of ordinary communication frequencies of from zero cycle up to about 2,000 cycles (including the Morse channel as well as the telephone channel) to he stepped up to a higher level, for instance, that corresponding to the 20,- 000 cycle channel, we then have this frequency band of zero to 2,000 cycles referred to the frequency of the carrier channel; for instance, for the 20,000 cycle channel the frequency range extends from the carrier frequency, both up and down the scale to the extent of 2,000 cycles.

As indicated above, the carrier frequency when modulated by a lower frequency is changed in frequency in both a plus and minus direction by the value of the lower frequency, the.2,000 cycle range of the ordinaryv telephone channel causing the 20,000 cycle channel, for instance, to vary between extremes of 18,000 and 22,000 cycles. By eliminating one of the two hands by means of a band filter the other band extending, for instance, from 20,000 cycles down to 18,000 only, may be transmitted. In this transmitted band the range occupied by the Morse channel composited on the telephone channel would be 20,000 cycles minus the telegraph band (zero to say, 100 cycles), or down to about 19,900 cycles. I The lower frequency edge of the telephone band would commence at, say, 19,700 cycles and extend down to about 18,000 cycles.

This elevation of the' composited frequency range from, say, zero to 2,000 cycles up to a band referred to a carrier frequency, such as 20,000 cycles, is accomplished by modulation in the usual manner. Similarly, the stepping down at the receiving end of this composite frequency band is done by demodulation. The several signaling currents imposed upon the same channel may be separated at low frequency ing ordinary telephone circuits.

In order to utilize signaling methods involving the transmission of telegraphic signals by direct currents of opposite polarfrequency each time the modulating telegraph signal changes polarity. Similarly, a demodulator is provided to translate a carrier current having constant amplitude and frequency, but reversed in phase at different intervals, into direct currents whose signs change with each phase reversal of the carrier frequency.

The invention may now be'more fully understood from the following detailed description when read in connection with the accompanying drawings, Figures 1 and 2 of which constitute circuit diagrams illustrating. different embodiments of the invention.

Referring to Fig. 1, ML designates atransmission line on which may be superimposed a number of carrier channels. The main transmission line ML is associated with the terminal car rier apparatus through a balanced transformer 10 of a well known type and a balancing net work or artificiahline MN. The terminal apparatus includes a common transmitting circuit TL and a common receiving circuit RL connected to the main line ML through the transformer and artificial line arrangement in such a manner that the two circuits will be conjugate with respect to each other; that is, will be so related thatan electrical disturbance arising in the one circuit will not affect the other. A plurality of transmitting channels, such as TL and TL, are associated with the com mon transmitting circuit TL, and similarly, a plurality of receiving channels, such as RL and EL are associated with the common circuit RL.

A telephone transmission line L is associated with the transmitting and receiving channels TL and RL,, through circuits 13 and 14-, respectively, the line L being connected to the circuits 13 and 14 through a transformer arrangement 11, similar to the transformer 10 already described and said line being balanced by an artificial line or net work N,

The transmitting channel TL includes a modulator M,, a filter TF, and amplifier TA, and a filter TF The filters TF and TF, are of the general type illustrated and described in the U. S. patents to George A. Campbell Nos. 1,227,113 and 1,227,114 dated May 22, 1014. Each of these filters is dc-' signed to transmit a band of frequencies ex tending fromthe basic frequency assigned to that channel down to a frequency differing from the basic frequency by a frequency corresponding to the upper limit employed 1916, or in 'the patent to John E. Carson, No.

1,343,307 issued J une 15, 1920.

The transmitting channel TL, includes a modulator M,, band filters TF, and TF, and amplifier TA,. The modulator M, is similar to the modulator M, already referred to and the amplifier TA, may be substantially the same as the amplifier TA,. The filters TF, and TF, will be of the same character as the filters TF, and TF, already referred to, but will be so designed as to transmit an equal range of frequencies at a different position on the broad frequency scale. For instance, if the frequency assigned to the channel TL, is 15,000 cycles, thesefilters may be arranged to transmit frequencies lying between 13,000 and 15,000 cycles.

The receiving channel BL, includes a detector D,, receiving amplifier RA, and high frequency bandfilter RF,.; The filter RF, and the amplifier RA, may be practically identical in construction with the filter T F,

and, the amplifier TA, of the transmitting channel TL,. The detector or demodulator D, may be of any well-known type, but is preferably of the duplex vacuum tube type illustrated and described in the patent to John R. Carson, No. 1,343,308 issued June 15, 1920. p

The circuit 14 which associates the telephone line L, with the receiving channel RL, may be provided with a low frequency filter RF,. This filter may likewise be of the general type disclosed in the patents to Campbell above referred to and should preferably be so designed as to transmit a band of frequencies extending over the range of frequencies employed in ordinary telephonic transmission, but excluding frequencies above and below said range.

The receiving channel BL, is provided with a filter RF, and an amplifier RA,,similar in all respects to the corresponding elements inthe receiving channel RL A de modulator or detector D, is also provided which is similar to the demodulator. D, already described in so far as it functions to detect telephonic currents. In order todetect- Morse currents, however, the demodulator D is provided with a differentially wound of this channel be taken'as 20,000

relay 15, having one winding in each half of the balanced output circuit. The opera tion of this relay in detecting Morse impulses will be more fully described hereinafter. The circuit 1st includes a low frequency filter RF, similar in all respects to the filter RF already described. V

The several demodulators or detectors used in the system here.n disclosed, preferably operate in accordance with the socalled homodyne principle and therefore each ,demodulator is supplied with carrier oscillations of the same frequency as the modulator. The several carrier frequencies maybe supplied in any Well-known manner, but preferably the frequency control system disclosed in the applcation of B. W. Kendall, Serial No. 130,350 filed November 5, 1916 may be used for this purpose. This frequency control system, since it forms no part of the present invention,is not illus-' trated in its entirety, but includes suitable means for impress ng the frequencies which correspond to the several carrier channels upon a common circuit 16. The individual frequencies are then selectively transmitted through selective circuits which .may constitute filtering. means of any well-known t pe, tfined circuits, such as CF, and CF, Am-

plifiers such as CA, and CA, areprovided for the several channels in order to amplify the carrier frequency selected from the common circuit 16. These amplifiers may be of any well-known type but are preferably of the same type as the amplifiers TA, and TA, already referred to. From the output circuit of the amplifier CA, a branch circuit 17 extends to the common conductor of the duplex input circuit of the modulator M,. A parallel branch 18 in a similar manner extends to the common conductor of the dupleX input circuit of the corresponding demodulator D,. The modulatoriM, and demodulator D, are supplied with carrier oscillations from the output circuit of the amplifier CA, through similar circuits 19 and 20.

In order that the transmitting channel TL, and the receiving channel RL, may be utilized for the transmission of signaling currents of a character other than the telephone currents transmitted from the line L,, a line L,, which may be any .low frequency line, such as a'Morse line, is associated with theinput circuit of the modulator M, and the output circuit of the demodulator D, through circuits 21 and 22, respectively. The Morse line L, is provided with a receiving relay 23, comprising balanced windings 24 and an armature 25 under the con- .trol of which positive and negative impulses corresponding to units of a telegraph code may be transmitted over the circuit 21 to the modulator M,. The receiving circuit but are herein illustrated as simply '22 leading from the output of the demodulator D is bridged across the mid points of the windings 24; so that impulses transmitted over this circuit from the demodulator will not actuate the receiving relay 23, an artificial line M being provided for the line L, in order to insure that the two halves of the relay 23 will be balanced. The circuit 21, being connected directly to the grids of the two tubes of the modulator M will function to unbalance the modulator so that high frequency currents of one phase will be transmitted when a direct current of one polarity is impressed upon the circuit 21,

while high frequency currents of opposite phase will be transmitted when a direct current of opposite polarity is impressed upon the circuit 21. Similarly, the outgoing circuit 22, connected to the two plates of the two tubes of the demodulator D will have a direct current of one sign impressed thereon by the output circuits of the two tubes when the applied carrier frequency from the channel RL has one phase relation with respect to the locally supplied carrier. while a direct current of opposite sign will be supplied to the circuit 22 when the carrier from the circuit RL is opposite in phase.

A slightly different arrangement is shown in connection with the transmitting channel TL and receiving channel RL In this case a Morse l'neL, of a well-known type having a grounded return is illustrated. This Morse line terminates in the usual duplex set, including the balancing artificial line N and receiving polar relay 26 bridged across neutral points of inductances 27 and 28. .Impulses received by the differential relay 15 of the demodulator D are transmitted over a conductor 29 to the mid point of the inductances 27 and 28 so that the receiving polar relay 26 is unaffected thereby. In order to transmit impulses received over the Morse line L to the modulator M a relay 30. is PIOVidBd under the control of the receiving polar relay 26. The relay 30, by means of its armature, controls an auxiliary connection from the output of the amplifier CA whereby carrier oscillations may be impressed upon the modulator M through the winding 31 which is cumulatively associated with the two halves of the input circuit of said modulator.

. It will be noted that certain details of the apparatus associated with the receiving and transmitting channels TL and RL differ from corresponding elements associated with the channels TL, and RL,. The two sets of apparatus are thus dillerently illustrated in order that two modifications of the invention may be disclosed without unnecessary duplication of the circuit diagram, and it will therefore be understood thatin practice the channels may include apparatus of different types, as illustrated, or all the channels may include identical apparatus of either type. 1

Further details of the apparatus may now be best understood from a description of the operation which is as follows:

Telephone currents incoming from the line L, are transmitted through the transformer 11 to the circuit 13. From this circuit the low frequency variations are impressed upon the grids of the two vacuum tubes of the modulator M through a trans former 32. At the same time oscillations of v I high frequency oscillations vary in accord-v ance with the low frequency telephone variat ons and are permitted to pass through the. transformer 33 to the transmitting channel TL' These modulated oscillations are passed through the filter TF amplified by the amplifier TA and are then transmitted through the filter TF to the common transmitting circuit TL. Similar modulated carrier currents may be transmitted from other transmitting channels upon the com,- mon circuit TL," from which the several modulated frequencies are passed through the transformer 10 to the main transmission line ML.

Modulated carrier oscillations transmitted over the line ML from a distant station are received into the common receiving circuit RL. From this circuit modulated oscillations corresponding to the several channels are selected into the proper receiving channels through the filters, such as RF RF' etc. The modulated carrier oscillations passing throughthe filter RF are amplified by the amplifier RA and are then im-.

pressed through the transformer 34 upon the input circuit of the demodulator D Normally, theinput circuit of this demodulator is supplied with oscillations from the output circuit of the amplifier CA 'through the circuit 18, the frequency of these oscillations being the same asthat of the carrier oscillations, which after modulation at the distant station, were transmitted over the line ML and passed through the filter RF Normally, the local oscillations produce no effect upon the demodulator since the circuit is balanced. As soon as modulated oscillations are impressed through the transformer 34, however, the demodulator is unbalanced thereby, so that low frequency telephonic variations corresponding to the telephone currents, in accordance with which the carrier oscillations were modulated at the distant station, are transmitted through the transformer 35 to the circuit 14. The resultant telephonic currents are passed through the low frequency filter RF, and are then transmitted over the telephone line L Simultaneously, with the operations above described, Morse currents incoming from the Morse line L, may actuate the receivcarrier,

ing relay 23 to apply positive and negative potential differences between the points 36 and 37 of the modulator M Normally, the two tubes being balancedf a carrier frequency determined by the "-circuit 17 will flow in the output circuit of each tube, the two currents being, however, of equal amplitude and opposite phase relation so that no current is transmitted through the transformer 33. When, however, the two tubes are unbalanced by a direct current flowing in the c rcuit 21 in one direction, the ampli tude of the carrier frequency in the output circuit of one of the tubes will be greater than that of the other, so that a resultant whose amplitude is determined'by the amount of the unbalance, and. whose phase is determined by the tube through which the greatest current flows, will be transmitted through the transformer 33. If the tubes, however, be unbalanced by current flowing in the circuit 21 in the o posite direction then the carrier current owing in the other tube will have the greatest amplitude and the resultant current transmitted through the transformer 33 will be of opposite phase, its amplitude, of course, depending upon the amount of the unbalance, if the direct currents of the two s'gns flowing in the circuit 21 be of equal amplitude the carrier frequency transmitted through the transformer 33 will be of constant amplitude and frequency, but a change in phase will occur each time the direct current in the circu't 21 changes sign. 'Actu- .Morse variations.

ally, the oscillations passing through the transformer 33 will have superimposed thereon the telephonic variations dueto the telephone currents transmitted over the circuit 13 so that the oscillations transmitted through the filter TF will be modulated in accordance with a complex wave, which is the result of telephonic variations and the Considering now that carrier currents of frequency corresponding to the receiving channel BL having a constant amplitude determined by a Morse impulse at a distant station, are being transmitted from the distant station over the line ML. Such oscil-. lations after passing over the common circuit RL and through the filter RF are amplified by. the amplifier RA and are imfrequencv.

mally at the same potential will have a constant potential difference impressed upon them so that a direct current flows over the circuit 22 to the Morse line L, in one direction. The direction of this current flow will depend upon the phase difference between the oscillations impressed upon the modulator from the receiving channel RL and from the circuit 18 and the direct current will therefore flow continually in one direction as long as there is no phase change in the incoming oscillations. When, however, oscillations of the same frequency but opposite in phase are impressed upon the demodulator, the potential difference betweenfithe plates of the two demodulating tubes will be opposite in sign to that just described, and a direct current will therefore flow in the circuit 22 to the Morse line in'the opposite direction;

The maintenance of a proper phase relation between the two sets of oscillations is desirable in order to secure an effective working of the apparatus. If, for instance, the carrier oscillations entering the dem dulator from the line and representing the 'direct current Morse signalof one sign'happento be a 90 out of phase, with respect to the oscillations from the circuit-18, no I). C. unbalance current fiow would result in the output circuit of the demodulator and the Morse D. C. would not be received. The efficiency of demodulation for D. C. output current is a maximum when the carrier supply bears either a zero or a 180 phase relation to the unmodulated component of the received carrier current but in the one case the resultant 'direct current will be of one sign and in the other case the resultant direct I current will be of oppos te sign. In short, some direct current will flow in' the circuit 22 for any phase relation other than 90 degrees between the locally. supplied carrier and the incoming carrier frequencv. The direction of this direct current will change if, for a given phase relation between 'the locally supplied carrier and the incoming the phase an le of the incoming frequency he chan ed 180 degrees. For a given amplitude of the incominq carrier frequency the amplitude of the direct current in the onedirection or the other willincrease. re ching the maximum when a zero phase difference exists between the incoming carrier and the locally sup lied carrier for direct current in one direction. and when a phase difference of 180 degrees exists between the incoming and locally supplied carriers for direct current in the opposite direction. In order to maintain proper phase relations between the incoming and locally supplied carriers a transformer-38 having its primary winding shunted by a. condenser 39 is included in the circuit 18,

so that by varying the capacity of the conbetween the points 40 and 4-1 of the demodu-- lator, these potential differences correspond ing to a variable current which is a resultant of superimposing a low frequency telephone current upon a D. C. Morse current. The

telephone variations pass through the transformer 35 t0 the circuit 14 and ,are transmitted through the filter RF, to the line L The filter .RF, does not permit the Morse current components to be passed to the line L and, consequently, the D, C. Morse components are transmitted over the circuit 22 to the Morse line L,'.

The operation of the apparatus associated with the transmitting channel TL and receiving channel RL so far as telephone transmission is concerned, is substantially the same as described with reference to the channels TL and RL,, the only difference being that the carrier oscillations forthese channels are of a frequency sufficiently different from that of the other channels so that proper selectivity between the several channels may be secured by the filters. Morse .currents received over the line L however, actuate the receiving relay 26, which in turn controls the relay 30. In response to a Morse impulse the relay 3O closes a connection over its back contact from the output of the amplifier CA to the winding 31 of the transformer 42. Carrier oscillations of constant amplitude are therefore passed through the modulator M to the transmitting channel TL so long as the Morse impulse persists. These oscillations will have superimposed thereon carrier oscillations modulated in accordance with telephone currents transmitted over the circuit from the receiving channel RL are im pressed upon the demodulator, the two tubes are unbalanced and the currents flowing 1n the two wndings have different values so 1 that the relay 15 acts as a pole changer to transmit Morse impulses over the circuit 29 to the Morse line L The windings of the differentialv relay 15 have sufficient im- U peclance to substantially prevent telephone variations which are detected by the demodulator D from flowing through the relay and affecting its operation. To further assist in separating the Morse currents from the telephone currents condensers are pro-- vided in each plate circuit in shunt with the windings of the relay 15, these condensers offering a low impedance path for telephone currents. The telephone variations pass through the transformer 44 and after transmission through the filter RF, are impressed upon the telephone line L In order to maintain a proper phase relation between the unmodulated components of the received carrier currents which correspond to the Morse signals, and the carrier oscillations impressed upon the detector D from the circuit 20, a transformer 45 and a condenser 46 are included in thelatter circuit, these elements functioning in the same mannor as "the elements 38 and 39 of the carrier channel first described.

Fig. 2 illustrates certain modifications of the apparatus shown in Fig. 1, correspondmg elements in-the two figures being designated by the same reference characters. The arrangement shown in Fig. differs from that of Fig. 1, principally, in the fact that the low frequency telephone line is composited so that the Morse signals are transmitted over the same line as the telephone signals. The line L,, for instance, is used in transmitting both telephone and telegraph signals and at the carrier terminal is divided into two' branches, one branch 47 transmitting the telephone currents and the other branch 48 transmitting telegraph currents. In order to prevent the telegraph currents from flowing into the branch 47, a filtering arrangement- 49 of a well-known construction is provided. Similarly, a filter-- ing arrangement 50 is provided in the branch 48 to prevent telephone currents from fiowlng over thlsbranch.

The telephone branch -17 is associated through a transformer 11. with circuits 13 and 14 leading to the modulator M and the demodulator D, as in Fig. 1. In order to associate the telegraph branch 48 with the modulator and demodulator the receiving relay 23 and the circuits 21 and 22 are pro-. vided as in -Fig. 1. Circuits 21 and 22 are providedwith filtering arrangements 51 and 52 similar to the filtering arrangement in order to prevent telephone currents from the circuits 13 and 14 from reacting in-said circuits, 21 and 22. In a similar manner the telephone branches 13 and 14 are provided with filtering arrangements 53 and 54 similar to thafiltering arrangement 49 to keep out the telegraph currents. A balancing artificial line or net work N is' provided for halancin the apparatus associated with the branch 4 beyond the filtering arrangement 49, the latter element being balanced by an equivalent filtering arrangement 55. Similarly, a filtering arrangement 50 is balanced with respect to the telegraph receiving relay 23 by means of an equivalent filtering arrangement 56, while the net work N is provided for balancing the apparatus associated withthe circuit 48 beyond the filter 50.

Telephone and telegraph currents transmitted over the line L are separated through the branches 47 and 48, respectively, due to the action of the filtering arrangements 49 and 50. The telephone currents are transmitted through the transformer 11, over the circuit 13, through the filtering arrangement 53 and through the transformer 32 to the modulator M Telegraph currents actuate the receiving relay 23 so that D. C. telegraph impulses of opposite signs are transmitted over the circuit 21 to the modulator M The telephone and telegraph currents are combined in the modulator M, in the same manner as described in connection with Fig. 1, and after being translated into high frequency currents are filtered, amplified and then transmitted over the main line ML to a distant station.

Corresponding high frequency currents transmitted from a distant station over the line ML flow over the common receiving circuit RL and are selected through the filter RF, they are amplified by the a'n'iplifier HA These high frequency currents'rcact upon the demodulator I) with oscillations of the proper carrier frequency from the circuit 18 so that low frequency potential ditlerences appear between thc'pomts 40 .and 41 of the detector 1),, which potential differences correspond to thecomhincd telephone and Morse currents in theirlow fre quency state. -The telephone currents are transmitted through the filtering arrangement'54 into the circuit 14, and after passing through the low frequency filter RF, are transmitted over the branch 47 to the line L,.

into the receiving channel RL where The Morse components on. the other hand pass through the filtering arrangement 52 to the circuit 22 from which point they are transmitted over the branch 48 to the line L,.

The arrangement described in connection with the transmitting-and receiving channels TL and BL, of Fig. 2 provides for the separation of the Morse and telephone currents before modulation and after detection. A slightly modified arrangement is shown in connection with the transmitting and receiving channels Tri and HA in which the telephone and Morse components remain com bined, at all times, both in their low frequency and high frequency states. In this case the line L is divided. into two branches 57 and 58 including balanced transformer arrangements 59 and 60 respectively. Beyond the transformer arrangements the circuits 57 and 58 again merge and at their junction point an artificial line or net work N is provided 1 for balancing the line 1],. The transmitting circuit 13, which in this case is used for impressing both Morse and telephone currents upon the modulator M is connected across the branch 57 at the mid points of the balanced transformer arrangement 59. Similarly, the receiving branch 14 which assoc-iates the demodulator D with the line L is connected across the branch 58 at the mid points of the transformer arrangement 60. The circuit 14 also transmits both telephone and Morse currents. By means of the a rangement above described the circuits .3 and 14. are rendered conjugate with respect to each other so that electrical variations arising in the one circuit donot afi'ect-theother.

Telephone and Morse currents flowing over the line L are transmitted through the bal-v anced transformer arrangement into the circuit 13 and from this circuit are impressed upon the modulator M thereby modulating ing circuit RL and are filtered through the filter RF into the receiving channel RL Upon being amplified by the amplifier RA the modulated oscillations are impressed through thetransformcr 43 upon the demodulator D Low frequency variations corresponding to the superposed Morse and telephone currents appear in the output circ-uit of the demodulator and are transi'nitted through the filter RF in the circuit 14 from which point they pass through the,balanced transformer arrangement to the line L. so arranged as to transmit frequencies lying between zero and the uppe-rlimit of fre quencies employed in ordinary telephonic transmission since the low frequency Morse currents must pass through this filter as well as the telephone currents.

As in the case of Fig. 1, two different forms of apparatus are disclosed in Fig. 2 in order to present different modifications without unnecessary duplication of the circuits. It will be understood, however, that in actual practice the apparatus of the different channels may be of the same character. Both of the arrangements shown in Fig. 2 function like the first arrangement described in connection with Fig. 1 in'so far as the translation of direct currents of opposite signs into carrier currents of opposite phases and vice versa are concerned.

By means of the arrangements heretofore described it is possible to superpose upon 5 each channel of a multiplex carrier system one or more signaling circuits, in addition to the low frequency telephone circuit. These signaling circuits, while illustrated as Morse telegraph circuits, may be signaling circuits of any desired character. Furthermore, while the invention has been illustrated as embodied in certain forms, which are' considered desirable from a practical standpoint, it will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without dcparting from the spirit of the invention as defined in the following claims.

What is claimed is:

, 1. In a signaling system, a transmission line adapted to transmit high frequency currents, a translating station at one end of said line, a modulating apparatus associated with said line at said station, means to transmit to said translating station telephone currents and low frequency unmodulated signaling currents of a different character, and means whereby said modnlating' apparatus is controlled by said telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance with said telephone and other signaling currents.

' 2. In a signaling system, a transmission line adapted' to transmit high frequency currents, a translating station at each end thereof, a modulating apparatus associatedwith said line at one station, a demodulating apparatus associated with said line at another station, means to transmit to said f'rst mentioned station telephone currents and unmodulated low frequency currents of a different character, means whereby said modulating apparatus is controlled by said The filter RF; in the circuit 13 should be telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance with said telephone and other signaling currents, and means at said second mentioned station whereby in response to said carrier currents said demodulating apparatus supplies telephone and other low frequency signaling currents simulating the currents transmitted to said first mentioned station.

3. In a signaling system, a transmission line adapted to transmit high frequency currents, a plurality of transmission channels associated with one end of the line, modulating apparatus for each channel adapted to supply to said line a plurality of different carrier frequencies characteristic of the individual channels, means to transmit to each of said channels telephone currents and unmodulated low frequency signaling currents of a different character, and means whereby the modulating apparatus of each channel is controlled by said telephone and other signaling currents to supply carrier currents to said transmission line modulated in accordance with said telephone and other signaling currents.

4. In a signaling system, a transmission line adapted to transmit high frequency currents, a plurality of transmission channels associated with each end thereof, modulating apparatus for each channel atone end of said transmission line, said modulating apparatus being adapted to supply to said line carrier frequencies characteristic of each channel, demodulating apparatus for each channel at the other end of the line, I

means to transmit to each of said first mentioned channels telephone currents and unmodulated low frequency signaling currents of a different character, means whereby the modulating apparatus of each channel iscontrolled by said telephone and other sig naling currents to supply carrier currents to said transmission line modulated in accord ance with said telephone and other signaling currents, means whereby said carrier currents are selectively transmitted to the several channels at the other end of the line, and means whereby the demodulating apparatus of each channelin response to said carrier currents supplies telephone and other low frequency signaling currents simulating the currents transmitted to the corresponding channel at the originating end of the transmission line.

5. In a signaling system, a main transmission line adapted for the transmission of high frequency currents, a second transmission lineadapted to transmit telephone currents and other low frequency signaling currents of a different character, means interconnecting said lines adapted to translate said telephone and signaling currents into high frequency currents, said means including a modulating apparatus and a source of carrier current, and means to impress said carrier currents, telephone and other signaling currents upon said modulating apparatus, whereby carrier currents are supplied to said main transmission line modulated in accordance with said telephone and other signaling currents.

6. In a signaling system, a main trans mission line adapted to transmit high frequency currents, a plurality of terminal transmission lines each adapted to transmit telephone currents and other low frequency signaling currents of a different character, channels interconnecting each terminal line with said main line and each including means adapted to translate said telephone and signaling currents into high frequency currents, said means comprising a modulating apparatus and a source of carrier current having a frequency characteristic of the channel to which it is assigned, and means to impress upon the modulating'apparatus of each channel the carrier fre quency characteristic of each channel together with the telephone and other signaling currents transmitted to the channel, whereby carrier currents from 'each channel are modulated in accordance with the telephone and other signaling currents.of each channel and then supplied to said main transmission line.

7'. In a signaling system, a main transmission line adapted for the transmission of high frequency currents, terminal transmission lincs at each end of said main line, said terminal lines being adapted to-transmit both telephone currents and other low frequency signaling currents of a different character, means interconnecting one of said terminal lines with said main line adapted -to translate said telephone and signaling currents into high frequency currents for transmission over said main line, said means including a modulating apparatus and asource of carrier currents, means to impress said carrier current, telephone and other signaling current upon said modulating apparatus, whereby carrier currents are supplied to said main transmission line modulated in accordance with said telephone and other signaling currents, means interconnecting said main line with the other terminal line adapted to translate said modu lated carrier currents into low frequency currents, said means including a demodulating apparatus so arranged that when modulated carrier currents are supplied thereto from said main transmission line telephone and other low frequency signaling currents will be. transmitted to said other terminal line.

' 8. In a signaling system, a main transmission .lineadapted for the transmission of high frequency currents, a plurality of of carrier current for each modulator having a frequency characteristic of the channel to whlch it is asslgned, means to impress upon the modulating devlce of each channel the carrier frequency assigned to each channel together with the talking and other signaling currents transmitted to each channel, whereby carrler currents from each channel are modulated in accordance with the tele-- phone and-other signaling currentsof each' channel and then supplied to said main line, channels interconnecting the terminal lines at the other end of the main line with said main line, demodulating devices for each channel adapted to translate said modulated carrier currents into low frequency currents. said demodulating devices being so arranged that when modulated carrier currents are supplied thereto from the said main transmission line telephone and other low frequency signaling currents will be transmitted to said terminal lines.

9. In a signaling system, a main transmission line adapted for high frequency transmission, a translating station associated with one end of said line, a terminal line leading to said translating station, means whereby telephone currents and other low frequency signaling currents may be transmitted over said terminal line, a modulator at said translating station, a source of carrier current therefor, means at said station to separate said telephone and other signaling currents and impress them upon the same modulator, whereby carrier currents modulated in accordance with said telephone and other signaling currents are supplied by said modulator, and means to transmit the, currents thus supplied to said main transmission line.

10. In a signaling system, a main transmission line adapted for high frequency transmission, a translating stations associated with one end of said line, a plurality of terminal lines leading to said translating station, means whereby telephone and other signaling currents may be transmitted over said terminal lines, a modulator for each terminal line at the translating station, a source of carrier current for each modulator having a frequency characteristic thereof, means at said translating station to separate the telephone and other signaling currents transmitted over the terminal lines and to impress said currents upon the modulator corresponding to each line, whereby carrier currents modulated in accordance with said telephone and other signaling currents are supplied by said modulators, and

means to transmit the currents thus supplied to said main transmission line.

11. In a signaling system, a main transmission line adapted for high frequency transmission, a translating station associated with one end of said line, a terminal line leading to said translating station, means whereby telephone currents and other low frequency signaling currents may be transmitted over said terminal line, a modulator at said translating station, a source of carrier current therefor, means at said second station, means to impress the modustation to separate said telephone and other signaling currents and impress them upon the same modulator whereby carrier currents modulated in accordance 'with said telephone and other signaling currents are supplied by said modulator, means to transmit the currents thus supplied to said main transmission line, a second translating station associated-with the other end of said main transmission line, a second terminal line leading to said second station, a demodulator at said second station, means to impress the modulated carrier currents upon said demodulator whereby said demodulator supplies the telephone and other signaling currents in accordance with which the carrier currents were modulated, means .to separate the telephone and other signaling currents thus supplied, and means to impress the separated currents upon said second terminal lme.

12. In a signaling system, a main transmission line adapted for high frequency transmission, a translating station associated with one end of said line, a plurality of terminal lines leading to said translating station, means whereby'telephone and other signaling currents' may be transmitted over said terminal lines, a modulator for each ter- -minal line at the translating station, a source of carrier currents for each modulator having a frequency. characteristic thereof, means at said translating station to separate the telephone and other signaling currents: transmitted over the terminal lines and to impress said currents upon the modulator corresponding to each line, whereby carrier currents modulated in accordance with said telephone and other signaling currents are supplied by said modulators, means to transmit the currents thus supplied to said main transmission line, a second translating station associated with theother end of said main line, a plurality of terminal lines leading to said second station, a demodulator corresponding to each terminal line at said lat-ed carrier currents upon said demoduline leading from said translating station,

a demodulator at said station, meanswhereby carrier currents modulated in accordance with telephone and other low frequency signaling currents of a different character may be transmitted over said main line to said demodulator, said demodulator in response thereto supplying telephone and other signaling currentsin accordance with which said carrier currents were modulated, means to separate said telephone currents from the other signaling currents, and means whereby both said telephone and othersignaling currents may be transmitted over said terminal line.

14:. In a signaling system, a main transmission line adapted for high frequency transmission, a translating station associated with one end of said line, a plurality of terminal lines leading from said translating 7 station, a demodulatorcorresponding to each terminal line at said station, means where by carrier. currents modulated 1n accordance with telephone and other low frequency signaling currents of a different character may be transmitted over said main line to said demodulators, said demodulators in response thereto supplying the telephone and other signalingcurrents in accordancewith which said carrier currents were modulated, means to separate the telephone currents from the other signaling currents, and means whereby both said telephone and other signaling currents may be transmitted over said terminal lines.

15. In a signaling system, a main trans-.

mission line adapted for the-transmission of high frequency currents, a terminal transmission line adapted to transmit low frequency currents, means interconnecting said lines adapted to translate high frequency carrier currents into low frequency signaling currents, said means including a demodulator, and' means .to impress upon said demodulator carrier currents modulated in accordance with telephone and other low frequency signaling currents of a different character, w e signaling currents in accordance with which the carrier currents were modulated'are supplied by the demodulator' and impressed upon said terminal line. 1

lIll

reby the telephone and other v 16. In a signaling system, a main transmission line adapted for thetransmission of high frequency currents, a plurality of terminal transmission lines adapted to transmit low frequency currents, means intercom necting each of said terminal lines with' .taneously transmitting a telephone current and a low frequency signaling current of a diiierent character over a transmission path to a modulating station, impressing both currents upon the same modulating apparatus together with a current of carrier frequency at said station, producing thereby a carrier current modulated in accordance with both the" telephone current and the other signaling current, and transmitting the modulated current over a second transmission path.

18. The method of superposing auxiliary signalin channels upon carrier current telephone ciannels which consists in simultaneously transmitting both a telephone current and a low frequency signaling current of different character over each of a plurality of transmission paths to a modulating station, impressing both currents from each path upon the same modulating apparatus at said station together with a carrier current whose frequency is assigned to the corresponding path, producing thereby a plurality of carrier currents each modulated in accordance with telephone currents and other signaling currents and transmitting the modulated currents simultaneously over a common transmission path.

19. The method of superposing auxiliary signaling channels upon carrier current telephone channels which consists in simultaneously transmitting a telephone current and a low frequency'signaling current of a different character over a transmission path to a modulating station, impressing both currents upon the same modulating apparatus together with a current of carrier frequency at said station, producing thereby a carrier current modulated in accordance with both the telephone current and theand other signaling currents in accordance with which the carrier current was modulated. V

20. The method of superposing auxiliary signaling channels upon carrier current telephone channels which consists in simultaneously transmitting a telephone current and a low frequency signaling current of a different character over a transmission path to a modulating station, impressing both currents upon the'same' modulating apparatus together with a current of carrier frequency at said station, producing thereby a carrier current modulated in accordance with both the telephone current and. the other signaling current, transmitting the modulated current over a second transmission path, then detecting the telephone and other signaling currents in accordance with which the carrier current was modulated. and transmitting both detected currents to the same transmission line.

21. The method of superposing auxiliary signaling channels upon carriercurrent telephone channels' which consists in simultaneously transmitting both a telephone current and a low frequency signaling current of different character over each of a plurality of transmission paths to a modulating station, impressing both currents from each path upon the same modulating apparatus at said station together with a carrier current whose frequency is assigned to the corresponding path, producing thereby a plurality of carrier currents each modulated in accordance with telephone currents and other signaling currents, transmitting the modulated currents simultaneously over a common transmission path, and then detecting from the several carrier currents the telephone and other signaling currents in accordance with which they were modulated. y

22. The method of superposing auxiliary signaling channels upon carrier current telephone channels which consists in simultaneously transmitting both a telephone current and a low frequency signaling current of different character over each of a plurality of transmission paths to a modulating station, impressing both currents from each path upon the same modulating apparatus at said station together with a carrier current whose frequency is assigned to the corresponding path, vproducing thereby a plurality of carrier currents each modulated in accordance with telephone currents and other signaling currents. transmitting the modulated currents simultaneously over a common transmission path, then detecting from the several carrier currents the telephone and other signaling currents in accordance with which theywere modulated, and transmitting each detected telephone current together with the corresponding carrier frequencies in accordance with both telephone currents'and auxiliary signal cur rents, transmitting the modulated frequencies to a distant point, detecting both the telephone and auxiliary signal currents from each carrier frequency, and transmitting to each of a plurality of transmission paths a detected telephone current and a corresponding detected auxiliary signaling current.

25. In a signaling system, a pair; of intercommunicating stations, a signaling channel at one station, a corresponding signaling channel at the other station, a modulator in a said first mentioned channel, a demodulator in said second mentioned channel, means to apply telephone currents to said modulator, whereby high frequency oscillations modulated in accordance with telephone currents may be supplied by said modulator for transmission to the distant station, a third station at a distant point, means to apply signaling currents of a character different from said telephone currents and received from said distant point to said modulator whereby high frequency oscillations modulated in accordance with said signaling currents may be supplied bysaid modulator for transmission to the distant station, and

means to impress the oscillations modulated in accordance with said telephone and signaling currents upon the demodulator in the corresponding channel at the distant station, wherebysaid demodulator translates the modulated oscillations into the telephone and signaling currents in accordance with which said oscillations were modulated.

26. In a signaling system, a pair of intercommunicatin stations, a plurality of sig naling channel s at one station, a plurality of correspondin signaling channels at the other station, a mo ulator in each of said first mentioned channels, a demodulator in each of said second mentioned channels, mcans'to apply telephone currents to each of said modula tors whereby high frequency oscillations modulated in accordance with said-telephone several demodulators in the corresponding.

channels at the distant station, whereby said demodulators translate the modulated oscil-- lations into the telephone and signaling currents in accordance with which the oscillations were modulated.

27. In a signal system, a pair'of intercommunicating stations, a signaling channel at one station, a corresponding signaling channel at the other station, a modulator in said first mentioned channel, means to apply telephone currents to said modulator whereby high frequency oscillations modulated in accordance with said tele hone currents may be supplied by said modulator for transmission to the corresponding channel at the distant station, a third .station at a distant point, and means to apply signaling currents of a characterdiflerent from said telephone currents and received from said distant point to said modulator, whereby high frequency oscillations modulated in accordance With said signaling currents may be supplied by said modulator 'for transmission to the corresponding channel at'the distant station.

28. In a signaling system, a pair of interlated in accordance with said signaling currents maybe supplied by said modulators for transmission to the corresponding channels at said distant station.

29. In a signaling system, a pair of inter-v communicating stations, a signaling channel at one station, a corresponding signaling channel at the other station, a demodulator in said second mentioned channel, and means whereby high frequency oscillations modumaaeso lated in accordance with telephone currents and other signaling currents difiering in character from telephone currents may be transmitted from said first mentioned channel to the distant station and applied to said demodulator, said demodulator functioning to translate said high frequency oscillations into the telephone currents and other signaling currents in accordance with which said oscillations were modulated, a third station at a distant point, and means to transmit said demodulated signal currents to said distant point.

30. In a signaling system, a pair of intercommunicating stations, a lurality of signaling channels at one 'sta on, a plurality of corresponding signaling channels at the other station, a demodulator in each of said second mentioned channels, and means whereby high frequency oscillations modulated in accordance with telephone currents and other signaling currents of a character different from telephone currents may be transmitted from each of said first mentioned channels to the distant station and applied to each of said demodulators, said demodulators functioning to translate said high frequency oscillations into the telephone currents and other signaling currents in accordance with which said oscillations were modulated, and means to transmit said demodulated signal currents to distant points.

31. A translating circuit for a carrier telegraph channel comprising a detecting device for detecting signal currents from modulated carrier currents, and a polarized relay having its windings conductively connected in series to the terminals of said device, said relay being responsive to detected signal currents of opposite signs.

32. In a carrier telegraph system, a translating device, an output circuit directly connected thereto, and means arranged to produce telegraphic code impulses of current of opposite polarities in said circuit in response to carrier currents impressed on said trans-- lating device. 3

33. In a carrier telegraph systenna carrier wave transmission path, a telegraph impulse circuit co operating with said path in the transmission of messa es, and means conductively connected to said impulse circu1t and responsive to received carrier waves for producing plus and minus telegraphic code current impulses in said impulsecircuit.

3t. lln a carrier telegraph system, means to produce code impulses of current of 9pposite polarities, means to translate said 1mpulses into alternating current, and means to .retranslate said alternating current into code impulses of current of opposite polarities for receiving purposes.

35. In carrier wave telegraphy, means to produce a carrier Wave of constant frequency and unvarying maximum amplitude, means to produce phase reversals in said Wave to transmit signals, and a translating device arranged to produce, under the control of the transmitted wave, direct current impulses reversed in polarity in correspondence with the phase reversals of said wave.

- 36. In a carrier telegraph system, means to transmit a continuous carrier wave, the phase of which is reversed at intervals denoting signals, a direct current telegraph receiving circuit, and a device arranged to translate said signals into direct current impulses of opposite polarities in said receiving circuit.

37. In a carrier telegraph system, means to transmit acontinuous carrier wave, the

phase of which is reversed at intervals denoting signals, a direct current telegraph receiving pircuit, and a device arranged to translate said signals into direct current impulses of opposite polarities in said rec iving circuit, said device being conducti ely connected to said receiving circuit.

38. In a carrier telegraph system, means till to generate a carrier wave of substantially constant frequency and amplitude, a. direct current circuit carrying impulses of positive and negative current, means under control of a positive impulse to transmit from said source a wave of a certain phase, and means under control of a negative impulse to transmit from said source a wave of opposite hase.

39. n a carrier telegraph system, means to transmit a substantially unbroken carrier wave of constant maximum amplitude, and means to derive from said wave for receiving purposes telegraphic code impulses of op osite polarities and current.

In testimony whereof I have signed my name to this specification this 28th day of July, 1919. v

, Lriorn ESPENSCHIED. 

